The problems associated with adherence and growth of bacteria on medical devices are well known. For example, catheterization with a “central line catheter” involves placing polyurethane or polyvinylchloride tubing into a blood vessel in the patient's chest while the other end of the tubing remains exposed to the hospital room environment and therefore to a variety of pathogens, potentially including drug-resistant pathogens. Frequently, this catheterization results in the life-threatening complication of system-wide infection of the blood. Research suggests that up to 90% of such cases originate in films of bacteria that adhere to catheter walls. Other types of catheters that are frequently used include urinary catheters, which are typically used with incontinent elderly patients, and are typically made of silicone and latex. Unfortunately, virtually all patients who have urinary catheters in place for 28 days or more develop urinary tract infections. Nearly all hospital-acquired systemic infections that are not associated with central line catheters are associated with urinary catheters. Treatment of urinary catheter-associated infections alone costs an estimated $1.8 billion annually.
Similar problems currently exist with orthopedic implants. Main causes of orthopedic implant failure include host inflammatory responses, and infection due to the formation of bacterial biofilms on the surface of the implants. Furthermore, studies have shown that the rate of infection associated with external fixators can be as high as 85%. Because metal pins and wires are being used more often in the treatment of orthopedic trauma, primarily for external fixation of bone fractures, any device improvements that decrease the rate of infections from joint prostheses or other metallic implants could have a significant impact on the quality of orthopedic healthcare.
A wide variety of surface modifications to medical devices have been tried with a goal of reducing infection rates of the modified medical devices. Such surface modifications include encapsulation of the medical device with a polymer to retard adherence by bacteria, and impregnation or coating of the medical device with antimicrobial agents. Representative examples of patents involving articles that have been coated or impregnated with anti-microbial drugs include U.S. Pat. No. 5,520,664 (“Catheter Having a Long-Lasting Antimicrobial Surface Treatment”), U.S. Pat. No. 5,709,672 (“Silastic and Polymer-Based Catheters with Improved Antimicrobial/Antifungal Properties”), U.S. Pat. No. 6,361,526 (“Antimicrobial Tympanostomy Tubes”), U.S. Pat. No. 6,261,271 (“Anti-infective and antithrombogenic medical articles and method for their preparation”), U.S. Pat. No. 5,902,283 (“Antimicrobial impregnated catheters and other medical implants”), and U.S. Pat. No. 5,624,704 (“Antimicrobial impregnated catheters and other medical implants and method for impregnating catheters and other medical implants with an antimicrobial agent”).
A functionally and structurally related class of glycopeptide antibiotics mediates antimicrobial activity by binding to the terminal D-alanine-D-alanine (D-Ala-D-Ala) of bacterial pentapeptide peptidoglycan precursors. This class of antibiotics has in common a three-dimensional structure containing a cleft into which binds peptide of highly specific configuration of D-Ala-D-Ala. Binding of D-Ala-D-Ala is believed to inhibit transpeptidation (cross-linking of D-Ala moiety with moieties on neighboring pentapeptides), thereby inhibiting cell wall growth. Antibiotics in this class of glycopeptide antibiotics include, but are not limited to vancomycin, avoparcin, ristocetin, teicoplanin, and their derivatives. For example, derivatives of vancomycin include, but are not limited to, multivalent vancomycins, pegylated vancomycin conjugates, norvancomycin, vancomycin disulfides, synmonicin, mono- or di-dechlorovancomycin, glutamine analogs of vancomycin (e.g., A51568B, and M43G), aspartic acid analogs of vancomycin (e.g., M43F, M43B), desvancosamine derivatives of vancomycin (e.g., A51568A and M43A, and corresponding aglycones), chlorine derivatives of vancomycin (e.g., A82846B, A82846A (eremomycin), orienticin A, A82846C), benzylic amino sugar derivatives of vancomycin (e.g., A82846B), N-acyl vancomycins, N-aracyl vancomycins, N-alkyl vancomycins (including but not limited to octylbenzyl, octyloxybenzyl, butylbenzyl, butyloxybenzyl, and butyl, derivatives). For a review of vancomycin-related glycopeptides, see, e.g., Nagarajan, Antimicrob. Agents Chemother. 1991, 35:605-609. Similar derivatives can be made using avoparcin, ristocetin, or teicoplanin, and methods well known in the art.
The need remains for a coating composition that can be applied to a medical device surface to inhibit growth of microorganisms. In addition, there remains a need for improved systems for localized delivery and extended release of antibiotics from surfaces of medical devices.